Systems and methods for organizing on-demand migration from private cluster to public cloud

ABSTRACT

Systems and methods for optimizing virtual migration includes determining a migration plan which includes migrating at least a virtual machine (VM) from a first origin node to a first candidate destination node over a network, determining a network migration cost for the migration plan, which includes determining a first relative network usage indicative of an amount of network traffic communicated over the network between the VM and each of one or more associated file storages when the VM is located on the first candidate destination node, and selecting to execute the migration plan based on the network migration cost.

BACKGROUND

The following description is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art.

A node (e.g., a host, a machine, a computer, and so on) can be configured to run one or more instances of virtual machines (VMs) by virtualizing or otherwise transforming hardware of the node into resources for the VMs. A node can further run one or more file storages (e.g., vDisks) that store files or data for the VMs located on the same node or VMs located on a different node. A given VM or vDisk can be migrated from an original host to a destination host. A VM and a vDisk can migrate due to various reasons such as but not limited to, reducing load of the original host when the original host becomes a hotspot, hypervisor upgrade of the original host, state cleanup of the original host, component change or upgrade of the original host, maintaining the original host, planned or abrupt power-off of the original host, and so on. In one example, VMs can be migrated to minimize inter-VM communications over a network. A VM can be migrated from an original host to a destination host by copying data (e.g., memory, virtualized hardware state data, and so on) associated with the VM from the original host to the destination host, such that the destination host can use hardware resources of the destination host to run the VM. In a VM live-migration, the VM (e.g., the compute portion) is migrated while the vDisk (e.g., the storage portion) may remain on a same node. In some cases, the data associated with VM is communicated from the original host to the destination host via a network.

Conventional systems migrate VMs while minimizing performance disruption, and ignore network traffic generated by migrating the VMs. Therefore, in some instances, a physical network card of a given node can be saturated by co-locating VMs that send or receive a considerable amount of data or co-locating VMs that rely heavily on remote I/Os. Network traffic significantly increases as the number of VMs that are migrated and the amount of data for associated with VM to be migrated increase. Increased network traffic can further result in network congestion and degradation of performance of nodes connected to the network. As such, there is a trade-off between an expected network traffic reduction resulting from the VM migration and the network usage due the VM migration process.

SUMMARY

In accordance with at least some aspects of the present disclosure, a method for optimizing virtual migration includes determining a migration plan that includes migrating at least a virtual machine (VM) from a first origin node to a first candidate destination node over a network, determining a network migration cost for the migration plan, which includes determining a first relative network usage indicative of an amount of network traffic communicated over the network between the VM and each of one or more associated file storages (which store files for the VM) when the VM is located on the first candidate destination node, and selecting to execute the migration plan based on the network migration cost.

In accordance with some aspects of the present disclosure, a migration server optimized for virtual migration includes a processing unit having a processor and a memory. The processing unit is configured to determine a migration plan that includes migrating at least a VM from a first origin node to a first candidate destination node over a network, determine a network migration cost for the migration plan, which includes determining a first relative network usage indicative of an amount of network traffic communicated over the network between the VM and each of one or more associated file storages (which store files for the VM) when the VM is located on the first candidate destination node, and select to execute the migration plan based on the network migration cost.

In accordance with some aspects of the present disclosure, a non-transitory computer readable media includes computer-executable instructions embodied thereon that, when executed by a processor of a migration server, cause the migration server to optimize virtual migration by determining a migration plan that includes migrating at least a VM from a first origin node to a first candidate destination node over a network, determining a network migration cost for the migration plan, which includes determining a first relative network usage indicative of an amount of network traffic communicated over the network between the VM and each of one or more associated file storages (which store files for the VM) when the VM is located on the first candidate destination node, and selecting to execute the migration plan based on the network migration cost.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, implementations, and features described above, further aspects, implementations, and features will become apparent by reference to the following drawings and the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system including various nodes supporting VMs and file storages (e.g., vDisks), in accordance with some implementations of the present disclosure.

FIG. 2A is a block diagram illustrating example locations of VMs and file storages before one or more VMs are migrated, in accordance with some implementations of the present disclosure.

FIG. 2B is a block diagram illustrating example locations of VMs and file storages after one or more VMs are migrated, in accordance with some implementations of the present disclosure.

FIG. 3 is a flowchart outlining operations for optimizing virtual migration, in accordance with some implementations of the present disclosure.

The foregoing and other features of the present disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several implementations in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative implementations described in the detailed description, drawings, and claims are not meant to be limiting. Other implementations may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

Implementations described herein relate to a scheme for optimizing virtual migration of a VM or a file storage (e.g., a vDisk). Applicant has observed that conventional VM systems have various technical problems related to migrating VMs and file storages, including and not limited to increased network traffic, poor I/O latency, and poor network performance after VMs/file storages are migrated. These technical issues result from the conventional VM systems' failure to account for network traffic between a VM and a file storage (e.g., a vDisk) associated with (e.g., storing files or data for) the VM. That is, conventional systems consider the short-term benefits of migration (e.g., load balancing) and neglects any long-term effect of such migration on network usage, resulting in poor network performance after the migration.

Implementations described herein provide various technical solutions to such technical problems by minimizing network usage with respect to migration of a VM or a file storage from an origin node to a destination node. An example indicator of network traffic is relative network usage (e.g., as calculated based on an I/O rate over a network) between a VM and an associated vDisk. When a VM is located on a same node as an associated vDisk (e.g., the VM and the associated vDisk are co-located on the same node), the relative network usage is 0 given that the I/O operations between the VM and the associated vDisk are local to that node. When a VM is located on a node different from that on which the vDisk is located (e.g., the VM and the associated vDisk are not co-located), the relative network usage can be determined, for example, by multiplying the I/O rate between the VM and the associated vDisk over the network by a length of time (e.g., a stability period). The implementations described herein factor the relative network usage with respect to the file storages of the VM in determining whether a particular migration plan (including migrating at least a VM and/or migrating at least a file storage) should be executed. In some examples, multiple migration plans can be determined (e.g., based on suitable load balancing algorithms), and the one having the lowest network migration cost is selected. The network migration cost includes at least the relative network usage as described. As such, the implementations disclosed herein provide various improvements over conventional systems, including optimizing efficiency of virtual migration of a VM or a file storage by reducing network traffic related to I/O management, lowering storage I/O latency for VMs, improving I/O rate capabilities for sequential I/O, and so on.

FIG. 1 is a block diagram of a system 100 including various nodes (e.g., nodes 120 a and 120 b) configured to support VMs 122 a, 124 a, 122 b, and 124 b and file storages 126 a and 128 a, in accordance with some implementations described in the present disclosure. Referring now to FIG. 1, the system 100 corresponds to a datacenter, a cluster, configured to provide computing and storage capabilities for one or more clients (not shown). Services commensurate with the VMs 122 a, 124 a, 122 b, and 124 b can be provided to the clients under respective SLAs, which may specify performance requirements. As shown, the system 100 includes a plurality of nodes such as but not limited to, the nodes 120 a and 120 b for provisioning the VMs 122 a, 124 a, 122 b, and 124 b and the file storages 126 a and 128 a.

In some implementations, each of the nodes 120 a and 120 b may be a hardware device such as but is not limited to a server. For example, one or more of the nodes 120 a and 120 b may be an NX-1000 server, NX-3000 server, NX-6000 server, NX-8000 server, etc. provided by Nutanix, Inc. or server computers from Dell, Inc., Lenovo Group Ltd. or Lenovo PC International, Cisco Systems, Inc., etc. In other examples, one or more of the nodes 120 a and 120 b may be another type of device that is suitable for use as a node within the system 100.

As shown, the node 120 a includes the VMs 122 a and 124 a, the file storages 126 a and 128 a, a hypervisor 130 a, a controller/service VM 132 a, a processing unit 134 a, and a memory unit 136 a. The node 120 b includes VMs 122 b and 124 b, a hypervisor 130 b, a controller/service VM 132 b, a processing unit 134 b, and a memory unit 136 b.

Each of the VMs 122 a, 124 a, 122 b, and 124 b is a software-based implementation of a computing machine. The VMs 122 a, 124 a, 122 b, and 124 b emulate functionalities of a physical computer. Specifically, the hardware resources such as but not limited to, the processing units 134 a and 134 b, the memory units 136 a and 136 b, storage, etc., of the underlying computers (e.g., the nodes 120 a and 120 b) are virtualized or transformed by a hypervisor (e.g., the hypervisor 130 a and 130 b) into the underlying support for each of the VMs (e.g., the VMs 122 a, 124 a, 122 b, and 124 b) that may run its own operating system (OS) and applications on the underlying physical resources in a manner similar to an actual computer. By encapsulating an entire machine, including CPU, memory, operating system, storage devices, and network devices, the VMs 122 a, 124 a, 122 b, and 124 b can be configured to be compatible with standard OSs (e.g. Windows, Linux, etc.), applications, and device drivers.

Each of the file storages 126 a and 128 a is a software-based implementation of a storage associated with (e.g., storing files for) a VM. An example of the file storages 126 a and 128 a is a vDisk. In some examples, a vDisk is a logical storage (e.g., including contiguous data chunks) virtualized from local storage devices (e.g., the memory unit 136 a).

In some implementations, a file storage can be co-located with (located on a same node as) the VM for which the file storage stores files or data. For example, the file storage 126 a may be associated with (stores files or data for) the VM 122 a. In that regard, the node 120 a is a hyperconverged node, which is capable of provisioning both a VM and a file storage. The VM 122 a is configured to handle communications (e.g., I/O operations) in connection with the file storage 126 a. Examples of types of I/O operations or actions include but are not limited to, cache reference, Dynamic random-access memory (DRAM) access, memory (e.g., Solid State Drive (SSD)) read, memory (e.g., SSD) write, disk seek, sending packets over the network 110, and so on. Given that the VM 122 a and the associated file storage 126 a are co-located, the I/O communications between the VM 122 a and the associated file storage 126 a are local to the node 120 a and therefore do not need to be routed via the network 110.

In some implementations, a file storage may be located on a different node as that of the VM for which the file storage stores files or data. For example, the file storage 128 a may be associated with (stores files or data for) the VM 122 b. In some examples, the node 120 b may be a compute-only node, which is capable of provisioning a VM but not any file storages. The VM 122 b is configured to handle communications (e.g., I/O operations) in connection with the file storage 128 a. Given that the VM 122 b and the associated file storage 128 a are not co-located, the I/O communications between the VM 122 b and the associated file storage 128 a are routed via the network 110.

While the VMs 122 a, 124 a, 122 b, and 124 b are shown to be located on the nodes 120 a and 120 b, fewer or greater number of VMs can be supported by each of the nodes 120 a and 120 b. While the file storages 126 a and 128 a are shown to be located on the nodes 120 a and 120 b, one of ordinary skill in the art can appreciate that each of the VMs 122 a, 124 a, 122 b, and 124 b is associated with one or more file storages (e.g., one or more vDisks).

The VMs 122 a, 124 a, 122 b, and 124 b may be managed by the hypervisors 130 a and 130 b. Each of the hypervisors 130 a and 130 b is a virtual machine monitor that allows a single physical server computer to run multiple instances of VMs. For example, the node 120 a can run the VMs 122 a and 124 a. The VMs 122 a and 124 a share the resources of that physical server computer (the node 120 a, including the processing unit 134 a and the memory unit 136 a), potentially across multiple environments. By running multiple VMs on a node, multiple workloads and multiple OSs may be run on a single piece of underlying hardware computer to increase resource utilization and manage workflow.

In some examples, the VMs 122 a, 124 a, 122 b, and 124 b are controlled and managed by the controller/service VMs 132 a and 132 b. The controller/service VMs 132 a and 132 b are configured to communicate with each other via the network 110 to form a distributed system. The hypervisors 130 a and 130 b may be configured to run virtualization software such as but not limited to, ESXi from VMWare, AHV from Nutanix, Inc., XenServer from Citrix Systems, Inc., etc., for running the VMs 122 a, 124 a, 122 b, and 124 b, for managing the interactions among the VMs 122 a, 124 a, 122 b, and 124 b, and for managing the underlying hardware of the nodes 120 a and 120 b. The controller/service VMs 132 a and 132 b and the hypervisors 130 a and 130 b may be configured as suitable for use within the system 100.

The controller/service VMs 132 a and 132 b are configured to manage, route, and otherwise handle workflow requests to and from the VMs 122 a, 124 a, 122 b, and 124 b. For example, the controller/service VM 132 a is configured to manage, route, and otherwise handle workflow requests to and from the VMs 122 a and 124 a. The controller/service VMs 132 a and 132 b are connected to the network 110 to facilitate communications among the nodes 120 a and 120 b, and thus to facilitate communications among the VMs 122 a, 124 a, 122 b, and 124 b. Although not shown, in some implementations, the hypervisors 130 a and 130 b may also be connected to the network 110.

The network 110 may include one or more of a cellular network, Wi-Fi, Wi-Max, ZigBee, Bluetooth, a proprietary network, Ethernet, one or more twisted pair wires, coaxial cables, fiber optic cables, local area networks, Universal Serial Bus (“USB”), Thunderbolt, or any other type of wired or wireless network, or a combination thereof. The network 110 may be structured to permit the exchange of data, instructions, messages, or other information among the nodes 120 a and 120 b (e.g., among the VMs 122 a, 124 a, 122 b, and 124 b, between a VM and a file storage, between the controller/service VMs 132 a and 132 b, and/or between the hypervisors 130 a and 130 b).

Each of the nodes 120 a and 120 b may be configured to communicate and share resources with each other via the network 110. For example, the nodes 120 a and 120 b may communicate and share resources with each other via a respective controller/service VM and/or a respective hypervisor. One or more of the nodes 120 a and 120 b may also be organized in a variety of network topologies, and each of the nodes 120 a and 120 b may be termed as a “host” or “host machine.” In that regard, each of the nodes 120 a and 120 b may have suitable network devices configured to allow the nodes 120 a and 120 b to communicate via the network 110.

Each of the nodes 120 a and 120 b may include processing units 134 a and 134 b, respectively, configured to execute instructions. The instructions may be carried out by a special purpose computer, logic circuits, or hardware circuits of the nodes 120 a and 120 b. The processing units 134 a and 134 b may be implemented in hardware, firmware, software, or any combination thereof. The term “execution” is, for example, the process of running an application or the carrying out of the operation called for by an instruction. The instructions may be written using one or more programming language, scripting language, assembly language, etc. The processing units 134 a and 134 b, thus, execute an instruction, meaning that they perform the operations called for by that instruction. The VMs 122 a, 124 a, 122 b, and 124 b, the hypervisors 130 a and 130 b, and the controller/service VM 132 a and 132 b can be implemented with the processing units 134 a and 134 b. Each of the nodes 120 a and 120 b may include memory units 136 a and 136 b, respectively, configured to store data. Examples of each of the memory units 136 a and 136 b include but are not limited to, DRAM, SSD, and the like.

In some implementations, a migration server 140 is configured to manage migration of one or more of the VMs 122 a, 124 a, 122 b, and 124 b and the file storages 126 a and 128 a in the manner described. In some implementations, the migration server 140 may determine a migration plan, which includes migrating at least one of the VMs 122 a, 124 a, 122 b, and 124 b and/or migrating at least one of the file storages 126 a-128 a for a given migration. The migration plan designates, for example, which of the VMs 122 a, 124 a, 122 b, and 124 b and the file storages 126 a and 128 a is to be migrated and which node is a candidate destination node. The migration server 140 is further configured to determine a network migration cost for the migration plan in the manner described. Based on the network migration cost, the migration server 140 determines whether to execute the migration plan.

The migration server 140 is connected to the node 120 a (e.g., the hypervisor 130 a) and the node 120 b (e.g., the hypervisor 130 b) over the network 110 for facilitating migrations. The migration server 140 includes processing capabilities, implemented in hardware, firmware, software, or any combination thereof to execute instructions. The instructions may be written using one or more programming language, scripting language, assembly language, etc. The migration server 140, thus, executes an instruction, meaning that the migration server 140 may perform the operations called for by that instruction.

In migrating a VM, the migration server 140 can copy or at least facilitates copying of state data (e.g., OS states) of the VM from an origin node to a destination node via the network 110. With respect to live connections, the migration server 140 can facilitate migration live connection on the VM via at least one of proxies and virtual private networks (VPNs) based on forwarding stubs. Similarly, the migration server 140 can copy or at least facilitates copying of data and files of the file storage from an origin node to a destination node via the network 110.

Implementations described herein reconciles benefits of migrating a VM or a file storage (e.g., hotspot reduction, load balancing, and the like) with a network migration cost. As used herein, a network migration cost is indicative of an overall change in network usage as a result of migrating one or more VMs and/or one or more file storages. In other words, by determining the network migration cost, the changes to global network traffic attributed to migrating a VM or a file storage is accounted for when determining whether to move a VM or a file storage to a destination node. A migration to a proposed destination node with the least increase in network migration cost (e.g., global network usage) or with the most decrease in network migration cost is preferable.

As used herein, a relative network usage is a parameter indicative of an amount of network traffic between the VM and a file storage (e.g., a vDisk) associated with the VM. Given that a given VM may have multiple file storages (e.g., multiple vDisks), network usage can be determined with respect to each of the multiple file storages. In that regard, the relative network usage concerning a VM is the sum of network usage determined with respect to all file storages that store files for the VM.

In some examples, the implementations described herein can be characterized using the following expressions. R(v, d) is a communication rate (e.g., the I/O rate in B/s) between VM v and vDisk d over a network. D(v) corresponds to a set of one or more vDisks associated with VM v. R(v, d) and D(v) are parameters obtainable from a data I/O manager of the hypervisor of the origin node. In some examples, p (v) ∈ N is a placement variable identifying of a next candidate destination node (out of a number of candidate destination nodes) that is being considered for hosting VM v. In some examples, p(d) ∈ N are placement variables identifying of a next candidate destination node (out of N candidate destination nodes) that is being considered for hosting vDisk d . In some examples, r(v, d) ∈ {0, R(v, d)} is the relative network usage rate (e.g., a rate of storage network traffic) between VM v and vDisk d. In some examples, the relative network usage rate r(v, d) can be characterized as:

r(v,d)=0⇄p(v)=p(d)   (1);

which means that when the VM v and vDisk d are co-located on a same candidate destination node, the relative network usage rate is 0. In some examples, the relative network usage rate r(v, d) can be characterized as:

r(v, d)=R(v, d)⇄p(v)≈p(d)   (2);

which means that when the VM v and vDisk d are located on separate nodes, the relative network usage rate is the communication rate R(v, d) between VM v and vDisk d over a network.

In some examples, responsive to a VM being migrated to another node, the network is used to copy the data (e.g., VM state data) of the VM from the origin node to the destination node to complete the migration. Similarly, data is copied over the network when a file storage is migrated. The amount of data to be copied over the network that is a part of the migration process itself (e.g., directly related to the migration) of a VM or a file storage is referred to as a direct migration cost. The direct migration cost may be a short-term network performance penalty.

In some examples, the direct migration cost of migrating a VM can be represented by m(v). An expression defining m(v) can be, for example:

∀v ∈V, m(v)=M(v) if f P(v)≈p(v),0 otherwise   (3);

where P(v) represents the origin node, and p(v) represents a next candidate destination node for hosting the VM. Expression (3) shows that when the origin node is not the next candidate destination node (e.g., when the VM is migrated from the origin node), the direct migration cost m(v) equals to M(v), which represents VM data copied when migrating to from P(v) to p(v). In some examples, M(v) corresponds to memory configured or allocated for the hosting the VM. In other examples, M(v) corresponds to memory actually used for hosting the VM instead of memory configured or allocated for the VM, given that the origin node may not transfer unused memory state of the VM to the destination node, as the memory at the destination node may be over-provisioned. The memory actually used for hosting the VM can be determined by subtracting the memory configured or allocated for the hosting the VM by a dirty page rate.

In some examples, the direct migration cost of migrating a file storage can be represented by m(d). An expression defining m(d) can be, for example:

∀d ∈D,m(d)=WSS(d) if f P(d)≈p(d),0 otherwise   (4);

where P(d) represents the origin node on which the file storage is located, and p(d) represents a next candidate destination node for hosting the file storage, as described. Expression (4) shows that responsive to determining that the origin node is not the next candidate destination node (e.g., when the file storage is migrated), the direct migration cost m(d) equals to W SS(d), which is used to denote data copied when migrating the file storage from P(d) to p(d). In some examples, WSS(d) is used to represent an amount of data transferred from P(d) to p(d) over time when migrating the file storage. WSS(d) can be collected by a data I/O manager of the hypervisor of the origin node. In some examples, direct migration cost of a file storage m(d) accounts for a data-locality loss as the file storage (e.g., a vDisk) and the VM may be temporarily located on separate nodes. In other examples, data-locality loss is not considered when determining m(d).

In some examples, the network migration cost can be defined as a sum of all changes in network usage for all VMs and file storages impacted by the migration, including, for each impacted VM, the direct migration cost of migrating a VM m(v), direct migration cost of migrating a file storage m(d), and relative network usage between VM v and vDisk. For example, the network migration cost (O) can be determined using the following expression:

0=Σ_(v∈V)(m(v)+Σ_(d ∈D(v))(m(d)+r(v, d)×T))   (5);

where the term r(v, d)×T represents relative network usage between VM v and vDisk d over a network, as the relative network usage is the product of the relative network usage rate r(v, d) and a stability period T. In some examples, a length of the stability period T is selected based on an average amount of time that the VM v or vDisk d resides on a given node before the next migration (e.g., as triggered by any load balancing features). In other examples, the stability period T is selected based on other suitable factors. In some examples, the stability period T has a predefined length (e.g., 0.5 hour, 1 hour, 1.5 hours, 2 hours, and the like).

The term m(d)+r(v, d)×T represents a sum of data communicated over the network with respect to a given file storage d, given that the direct migration cost of the file storage m(d) is added to the relative network usage between VM v and vDisk d over a network. The term Σ_(d ∈D(v))(m(d)+r(v, d)×T) represents that the sum of data communicated over the network with respect to a given file storage d is calculated for the entire set of file storages d ∈ D(v).

The term m(v)+Σ_(d ∈D(v))(m(d)+r(v, d)×T) represents the network migration cost with respect to a given impacted VM v given that the direct migration cost of a VM m(v) is added to the term Σ_(d ∈D(v))(m(d)+r(v, d)×T). The overall expression (5) represents that the network migration cost with respect to all impacted VMs are summed to obtain the network migration cost (O).

In additional implementations, expression (5) can be further augmented to take into account network communications among the VMs. For example, X(v, x) is a communication rate (e.g., data exchange rate in B/s) between VM v and another VM x over a network. With respect to each VM v, x(v, x) is determined for each VM x in communication with VM v, where x(v, x)=X(v, x) if VM v and VM x communicate over the network.

FIGS. 2A and 2B illustrate an example application of migration optimization involving the network migration cost, for example, as described using expressions (1)-(5). FIG. 2A is a block diagram illustrating example locations of VMs 220 a-220 c and vDisks 230 a, 230 b, 231 c, and 232 c before one or more VMs (e.g., VM_(a) 220 a and VM_(c) 220 c) are migrated according to some arrangements. FIG. 2B is a block diagram illustrating example locations of VMs 220 a-220 c and vDisks 230 a, 230 b, 231 c, and 232 c after one or more VMs (e.g., VM_(a) 220 a and VM_(c) 220 c) are migrated according to some arrangements. Referring to FIGS. 1-2B, node A 210 a is a node such as but not limited to, the node 120 b. For example, node A 210 a may be a compute-only node configured to support one or more VMs without supporting any file storages 0. Each of node B 210 b, node C 210 c, and node D 210 d is a node such as but not limited to, the node 120 a. For example, each of the nodes 210 b-210 d is a hyperconverged node capable of supporting one or more file storages in addition to any VMs.

As shown in FIG. 2A (prior to migration), VM_(c) 220 c is located on node A 210 a. VM_(b) 220 b and file storage (e.g., vDisk_(b) 230 b) associated with (e.g., storing files for) VM_(b) 220 b are co-located on node B 210 b. File storage (e.g., vDisk_(c1) 231 c) associated with (e.g., storing files for) VM_(c) 220 c is located on node C 210 c. VM_(a) 220 a, file storage (e.g., vDisk_(a) 230 a) associated with (e.g., storing files for) VM_(a) 220 a, and file storage (e.g., vDisk_(c2) 232 c) associated with (e.g., storing files for) VM_(c) 220 c are co-located on node D 210 d.

Some VMs in FIGS. 2A and 2B communicate (e.g., performing I/O operations) with an associated file storage via a network (not shown) such as but not limited to, the network 110. For example, as shown in FIG. 2A, VM_(c) 220 c communicates with associated file storages vDisk_(c1) 231 c and vDisk_(c2) 232 c via the network.

The example migration plan with regard to FIGS. 2A and 2B includes migrating VM_(a) 220 a to from node D210 d to node A 210 a and migrating VM_(c) 220 c from node A 210 a to node D 210 d. While two VMs 220 a and 220 c are migrated in the example migration plan shown in FIGS. 2A and 2B, one or more of the vDisks 230 a, 230 b, 231 c, and 232 c and be likewise migrated as part of a migration plan. Given that the network migration cost determination is concerned with relative network usage between a VM and a file storage, the network migration cost determination (e.g., the expressions (1)-(5)) is likewise applicable when a vDisk is migrated.

The nodes 210 a and 210 d are candidate destination nodes in the example migration plan with regard to FIGS. 2A and 2B. In some implementations, such migration plan is determined by the migration server 140 based on a suitable load-balancing algorithm, for example, in an attempt to reduce hotspots. In some implementations, such migration plan is determined by the migration server 140 based on based on a size of the VM and a size of available memory on the candidate destination node. For example, a horizontal length of a block representing each of the nodes 210 a-210 d represents a size of available memory on a respective one of the nodes 210 a-210 d. A horizontal length of a block representing each of the VMs 220 a-220 c represents a size of a respective one of the VMs 220 a-220 c. The size of a VM may be an allocated size or an actual size. Node C 210 c does not have sufficient available memory to support VM_(a) 220 a, thus VM_(a) 220 a can potentially be migrated to the nodes 210 a and 210 b. VM_(c) 220 c can potentially be migrated to any of the nodes 210 b-210 d.

For instance, the relative network usage between a VM and an associated file storage is minimal (e.g., 0) responsive to determining that the VM and the associated file storage are co-located on a same node because the communications between the VM and the associated file storage is performed locally without using a network. As shown in FIGS. 2A (prior to migration) and 2B (subsequent to migration), the relative network usage between VM_(b) 220 b and vDisk_(b) 230 b is 0 prior to migration and subsequent to migration because VM_(b) 220 b and vDisk_(b) 230 b are co-located on node B 210 b before and after migration of VM_(a) 220 a and VM_(c) 220 c. In that regard, the change of relative network usage concerning VM_(b) 220 b and vDisk_(b) in view of the proposed migration plan is 0.

As shown in FIG. 2A (prior to migration), the relative network usage between VM_(a) 220 a and vDisk_(a) 230 a is 0 because VM_(a) 220 a and vDisk_(a) 230 a are co-located before the migration of VM_(a) 220 a and VM_(c) 220 c. As shown in FIG. 2B (subsequent to migration), the relative network usage between VM_(a) 220 a and vDisk_(a) 230 a is greater than 0 because VM_(a) 220 a and vDisk_(a) 230 a are located on different nodes subsequent to the migration of VM_(a) 220 a and VM_(c) 220 c. In that regard, the change in relative network usage concerning VM_(a) 220 a in view of the proposed migration plan is the post-migration relative network usage between VM_(a) 220 a and vDisk_(a) 230 a.

As shown in FIG. 2A (prior to migration), the relative network usage between VM_(c) 220 c and vDisk_(c1) 231 c is greater than 0 because VM_(c) 220 c and vDisk_(c1) 231 c are located on separate nodes before the migration of VM_(a) 220 a and VM_(c) 220 c. As shown in FIG. 2A (prior to migration), the relative network usage between VM_(c) 220 c and vDisk_(c2) 232 c is greater than 0 because VM_(c) 220 c and vDisk_(a) 232 c are located on separate nodes before the migration of VM_(a) 220 a and VM_(c) 220 c.

As shown in FIG. 2B (subsequent to migration), the relative network usage between VM_(c) 220 c and vDisk_(c1) 231 c is greater than 0 because VM_(c) 220 c and vDisk_(c1) 231 c are located on separate nodes subsequent the migration of VM_(a) 220 a and VM_(c) 220 c. As shown in FIG. 2B (subsequent to migration), the relative network usage between VM_(c) 220 c and vDisk_(a) 232 c is 0 because VM_(c) 220 c and vDisk_(c2) 232 c are co-located subsequent to the migration of VM_(a) 220 a and VM_(c) 220 c. In that regard, the change of relative network usage concerning VM_(c) 220 c and vDisk_(c1) 231 c/vDisk_(a) 232 c in view of the proposed migration plans equals to the post-migration relative network usage between VM_(c) 220 c and vDisk_(c1) 231 c subtracted by a sum of the pre-migration relative network usage between VM_(c) 220 c and vDisk_(c1) 231 c and the pre-migration relative network usage between VM_(c) 220 c and vDisk_(c2) 232 c.

Based on a size of VM_(a) 220 a, VM_(a) 220 a can potentially be located on node B 210 b or node D 210 d (if VM_(b) 220 b or VM_(c) 220 c are migrated away from node B 210 b or node D 210 d to make room given the limitation on available memory). However, VM_(a) 220 a being located on node B 210 b or node D 210 d could increase the network migration cost if the network usage rate between VM_(c) 220 c and vDisk₂ 232 c is greater than VM_(a) 220 a and vDisk_(a) 230 a.

In addition, the migration plan as shown in FIGS. 2A and 2B may be selected to be executed in the scenario in which the relative network usage rate (e.g., the I/O rate) between VM_(c) 220 c and vDisk_(c2) 232 c is higher than the relative network usage rate (e.g., the I/O rate) between VM_(c) 220 c and vDisk_(c1) 231 c. A VM being co-located with an associated vDisk that has the highest relative network usage rate among all associated vDisks for that VM leads to a lower network migration cost, for example, as determined using expression (5). That is, as a consequence of the migration optimization as described herein, VMs having a lower relative network usage rate are preferred candidates for compute-only nodes, and a VM is placed on a node that hosts one of the associated vDisks having the highest relative network usage rate whenever possible.

FIG. 3 is a flowchart outlining operations for a method for optimizing virtual migration, in accordance with some implementations of the present disclosure. Additional, fewer, or different operations may be performed in the method depending on the implementation and arrangement. Referring to FIGS. 1-3, the method 300 includes monitoring network usage between all VMs and associated file storages in a given system (e.g., the system 100 or the system shown in FIGS. 2A and 2B) and determining VM/file storage placement that minimize network usage using the network migration cost scheme as described herein.

At 310, the migration server 140 monitors node usage for nodes (e.g., the nodes 120 a, 120 b, and 210 a-210 d) in a given system (e.g., the system 100 or the system shown in FIGS. 2A and 2B). Monitoring of node usage may be performed under a suitable load-balancing algorithm to reduce hotspots. For example, the migration server 140 may be in communication with each of the nodes in the system to receive usage data (e.g., CPU usage, memory usage, and the like) to determine whether a particular node is a hotspot.

At 320, the migration server 140 determines whether the node usage of one or more nodes exceeds a predetermined threshold. In one example, the predetermined threshold with regard to CPU usage is 85% of the total CPU capacity. In one example, the predetermined threshold with regard to memory usage is 100% of the total memory capacity. Blocks 310 and 320 are example triggers for determining the migration plan as described wih respect to block 330. Other triggers (e.g., other types of load-balancing) algorithms can be likewise implemented. Responsive to determining that the node usage does not exceed the threshold (320:NO), the method 300 returns to 310.

On the other hand, responsive to determining that the node usage exceeds the threshold (320:YES), the migration server 140 determines a migration plan to offload the hotspot nodes at 330. The migration plan (e.g., as shown in FIGS. 2A and 2B) may include migrating at least a VM from a first origin node (e.g., a hotspot node) to a first candidate destination node over a network (e.g., the network 110) and/or migrating a file storage from a second origin node (e.g., a hotspot node) to a second candidate destination node. The migration plan may identify VM(s) and/or file storage(s) to be migrated and a candidate destination node for each of the VM(s) and/or file storage(s) to be migrated. In some examples, the migration plan can be determined based on a load-balancing algorithm. For example, the VM(s) and/or file storage(s) to be migrated is previously located on a hotspot node. In some examples, the migration plan (e.g., the candidate destination nodes) can be determined based on a size of the VM/file storage and a size of available memory on each of the candidate destination nodes. That is, each candidate destination node for a particular VM/file storage has sufficient available memory to support that VM/file storage. In some examples, the migration plan (e.g., the candidate destination nodes) can be determined based on processing requirements (e.g., an amount of processing power needed when located on the origin node) of the VM/file storage and an amount of available processing power on each of the candidate destination nodes. That is, each candidate destination node for a particular VM/file storage has sufficient available processing power to support that VM/file storage.

At 340, the migration server 140 optimizes network efficiency of the migration plan by determining a network migration cost for the migration plan. The network migration cost can be determined using at least the expressions (1)-(5). For example, for each VM, the migration server 140 is configured to determine a first relative network usage indicative of an amount of network traffic communicated over the network between the VM and each of one or more associated file storages when the VM is located on a first candidate destination node. For each file storage, the migration server 140 is further configured to determine a second relative network usage indicative of an amount of network traffic communicated over the network between the file storage and an associated VM when the file storage is located on the second candidate destination node.

In response to determining that an associated file storage of is located on a node different from the candidate destination node, the network usage indicative of the network traffic between the VM and the file storage is greater than 0. In particular, the relative network usage is determined by multiplying a stability period by a relative network usage rate between the VM and the associated file storage in the manner described. The first relative network usage rate includes an I/O rate for communications between the VM and the associated file storage over the network. On the other hand, in response to determining that the VM and the associated file storage are co-located on the same candidate destination node, the relative network usage indicative of the amount of network traffic between the VM and the associated file storage is 0.

In some examples, the network migration cost includes at least a direct migration cost of migrating each VM. The direct migration cost of migrating the VM corresponds to an amount of data to be copied over the network in migrating the VM from the first origin node to the first candidate destination node. The direct migration cost of migrating the VM includes VM state data. As described, the direct migration cost of migrating the VM is 0 in response to determining that, in the migration plan, the VM remains on a same node as the first origin node on which the VM is currently located.

In some examples, the network migration cost includes at least a direct migration cost of migrating each of the one or more associated file storages and the relative network usage indicative of the amount of network traffic between the VM and each of the one or more associated file storages when the VM is located on the first candidate destination node. The direct migration cost of migrating each of the one or more associated file storages corresponds to an amount of data to be copied over the network in migrating each of the one or more file storages. As described, the direct migration cost of migrating an associated file storage is 0 in response to determining that, in the migration plan, the associated file storage remains on a same node as a current node on which the associated file storage is currently located.

At 350, the migration server 140 selects to execute the migration plan based on the network migration cost. In some examples, the migration server 140 selects to execute the migration plan in response to determining that the network migration cost is below a predetermined threshold. In some examples, the migration server 140 selects to execute the migration plan in response to determining that the migration plan has the least network migration cost among the network migration costs for all other proposed migration plans.

The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the examples disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

The hardware used to implement the various illustrative logics, logical blocks, modules, and circuits described in connection with the examples disclosed herein may be implemented or performed with a general purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Alternatively, some steps or methods may be performed by circuitry that is specific to a given function.

In some exemplary examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof If implemented in software, the functions may be stored as one or more instructions or code on a non-transitory computer-readable storage medium or non-transitory processor-readable storage medium. The steps of a method or algorithm disclosed herein may be embodied in a processor-executable software module which may reside on a non-transitory computer-readable or processor-readable storage medium. Non-transitory computer-readable or processor-readable storage media may be any storage media that may be accessed by a computer or a processor. By way of example but not limitation, such non-transitory computer-readable or processor-readable storage media may include RAM, ROM, EEPROM, FLASH memory, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of non-transitory computer-readable and processor-readable media. Additionally, the operations of a method or algorithm may reside as one or any combination or set of codes and/or instructions on a non-transitory processor-readable storage medium and/or computer-readable storage medium, which may be incorporated into a computer program product.

It is also to be understood that in some implementations, any of the operations described herein may be implemented at least in part as computer-readable instructions stored on a computer-readable memory. Upon execution of the computer-readable instructions by a processor, the computer-readable instructions may cause a node to perform the operations.

The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” Further, unless otherwise noted, the use of the words “approximate,” “about,” “around,” “substantially,” etc., mean plus or minus ten percent.

The foregoing description of illustrative implementations has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed implementations. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents. 

1. A method for optimizing virtual migration, comprising: determining a migration plan comprising migrating a virtual machine (VM) from a first origin node to a first candidate destination node over a network; determining a network migration cost for the migration plan comprising determining a first relative network usage indicative of network traffic communicated over the network between the VM and associated file storage when the VM is located on the first candidate destination node; and selecting to execute the migration plan based on the network migration cost.
 2. The method of claim 1, wherein the associated file storage comprise vDisks.
 3. The method of claim 1, wherein determining the migration plan comprises selecting the first candidate destination node for the migration plan based on a size of the VM and a size of available memory on the first candidate destination node.
 4. The method of claim 1, wherein determining the migration plan comprises selecting the first candidate destination node for the migration plan based on a load-balancing algorithm.
 5. The method of claim 1, wherein the first relative network usage is determined by multiplying a stability period by a first relative network usage rate between the VM and the associated file storage.
 6. The method of claim 5, wherein the first relative network usage rate comprises an I/O rate for communications between the VM and the associated file storage over the network.
 7. The method of claim 1, wherein the migration plan further comprises migrating a file storage from a second origin node to a second candidate destination node; and determining the network migration cost further comprises determining a second relative network usage indicative of network traffic communicated over the network between the file storage and an associated VM when the file storage is located on the second candidate destination node, wherein the file storage stores files for the associated VM.
 8. The method of claim 1, wherein the network migration cost comprises at least a direct migration cost of migrating the associated file storage and the relative network usage indicative of network traffic between the VM and the associated file storage when the VM is located on the first candidate destination node.
 9. The method of claim 8, wherein the direct migration cost of migrating the associated file storage corresponds to an amount of data to be copied over the network in migrating the associated file storage.
 10. The method of claim 9, wherein the direct migration cost of migrating a first associated file storage of a plurality of associated file storages is in response to determining that the first associated file storage remains on a same node as a current node on which the first associated file storage is currently located.
 11. The method of claim 1, wherein the network migration cost comprises at least a direct migration cost of migrating the VM; and the direct migration cost of migrating the VM corresponds to data to be copied over the network in migrating the VM from the first origin node to the first candidate destination node.
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)
 16. (canceled)
 17. A migration server, comprising: a processing unit having a processor and a memory, wherein the processing unit includes programmed instructions that when executed cause the processing unit to: determine a migration plan comprising migrating at least a virtual machine (VM) from a first origin node to a first candidate destination node over a network; determine a network migration cost for the migration plan comprising determining a first relative network usage indicative of an amount of network traffic communicated over the network between the VM and associated file storage when the VM is located on the first candidate destination node; and select to execute the migration plan based on the network migration cost.
 18. The migration server of claim 17, wherein the migration plan further comprises migrating a file storage from a second origin node to a second candidate destination node; and determines the network migration cost further comprises determining a second relative network usage indicative of network traffic communicated over the network between the file storage and an associated VM when the file storage is located on the second candidate destination node, wherein the file storage stores files for the associated VM.
 19. A non-transitory computer readable media includes computer-executable instructions embodied thereon that, when executed by a processor of a migration server, cause the migration server to optimize virtual migration by: determining a migration plan comprising migrating at least a virtual machine (VM) from a first origin node to a first candidate destination node over a network; determining a network migration cost for the migration plan comprising determining a first relative network usage indicative of network traffic communicated over the network between the VM and each of a plurality of associated file storage when the VM is located on the first candidate destination node; and selecting to execute the migration plan based on the network migration cost.
 20. The non-transitory computer readable media of claim 19, wherein the migration plan further comprises migrating a file storage from a second origin node to a second candidate destination node; and determines the network migration cost further comprises determining a second relative network usage indicative of network traffic communicated over the network between the file storage and an associated VM when the file storage is located on the second candidate destination node, wherein the file storage stores files for the associated VM.
 21. The non-transitory computer readable media of claim 19, wherein determining the migration plan comprises selecting the first candidate destination node for the migration plan based on a size of the VM and a size of available memory on the first candidate destination node.
 22. The non-transitory computer readable media of claim 19, wherein determining the migration plan comprises selecting the first candidate destination node for the migration plan based on a load-balancing algorithm.
 23. The non-transitory computer readable media of claim 19, wherein the first relative network usage is determined by multiplying a stability period by a first relative network usage rate between the VM and the associated file storage.
 24. The non-transitory computer readable media of claim 19, wherein the first relative network usage rate comprises an I/O rate for communications between the VM and the associated file storage over the network.
 25. The non-transitory computer readable media of claim 19, wherein the network migration cost comprises at least a direct migration cost of migrating the VM; and the direct migration cost of migrating the VM corresponds to an amount of data to be copied over the network in migrating the VM from the first origin node to the first candidate destination node.
 26. The non-transitory computer readable media of claim 25, wherein the direct migration cost of migrating the VM comprises VM state data.
 27. The non-transitory computer readable media of claim 19, wherein the migration plan further comprises migrating an additional VM over the network; and the network migration cost comprises an additional direct migration cost of migrating the additional VM.
 28. The non-transitory computer readable media of claim 27, wherein the network migration cost further comprises an additional relative network usage; and the additional relative network usage is determined by multiplying a stability period by an additional relative network usage rate between the additional VM and additional file storage storing files for the additional VM.
 29. The non-transitory computer readable media of claim 19, wherein in response to determining that the VM and a first file storage of a plurality of associated file storages are co-located on the first candidate destination node, the first relative network usage indicative of the amount of network traffic between the VM and the first file storage is
 0. 30. The non-transitory computer readable media of claim 19, wherein in response to determining that a second file storage of a plurality of associated file storages is located on a node different from the first candidate destination node, the first network usage indicative of the network traffic between the VM and the second file storage is greater than
 0. 31. The migration server of claim 17, wherein the associated file storage comprise vDisks.
 32. The migration server of claim 17, wherein determining the migration plan comprises selecting the first candidate destination node for the migration plan based on a size of the VM and a size of available memory on the first candidate destination node.
 33. The migration server of claim 17, wherein determining the migration plan comprises selecting the first candidate destination node for the migration plan based on a load-balancing algorithm.
 34. The migration server of claim 17, wherein the first relative network usage is determined by multiplying a stability period by a first relative network usage rate between the VM and the associated file storage.
 35. The migration server of claim 34, wherein the first relative network usage rate comprises an I/O rate for communications between the VM and the associated file storage over the network.
 36. The migration server of claim 17, wherein the network migration cost comprises at least a direct migration cost of migrating the associated file storage and the relative network usage indicative of network traffic between the VM and the associated file storage when the VM is located on the first candidate destination node.
 37. The migration server of claim 36, wherein the direct migration cost of migrating the associated file storage corresponds to an amount of data to be copied over the network in migrating the associated file storage.
 38. The migration server of claim 37, wherein the direct migration cost of migrating a first associated file storage of a plurality of associated file storages is in response to determining that the first associated file storage remains on a same node as a current node on which the first associated file storage is currently located.
 39. The migration server of claim 17, wherein the network migration cost comprises at least a direct migration cost of migrating the VM; and the direct migration cost of migrating the VM corresponds to data to be copied over the network in migrating the VM from the first origin node to the first candidate destination node.
 40. The migration server of claim 39, wherein the direct migration cost of migrating the VM comprises VM state data. 